tictactoe/main.cpp

#include <iostream>
#include <iomanip>

#ifdef _WIN32
#include <windows.h>
#endif

using namespace std;

const int N = 3;

struct userInput {
    bool ok;
    int zeile;
    int spalte;
};

struct gameState {
    bool running = true;
    char winner = ' ';
    char board[N][N];
    int filledCells = 0;
    // Per-player (0=X, 1=O) counters for rows, cols, and both diagonals.
    // Win-check is O(1): increment on each move, compare to N.
    int rowCount[2][N] = {};
    int colCount[2][N] = {};
    int diagCount[2] = {};
    int antiDiagCount[2] = {};
};

void render(const gameState &state) {
#ifdef _WIN32
    system("cls");
#endif
#ifdef linux
    system("clear");
#endif

    cout << "  | ";
    for (int j = 0; j < N; j++) cout << j + 1 << " | ";
    cout << endl;
    for (int i = 0; i < N * 4 + 3; i++) cout << "-";
    cout << endl;
    for (int i = 0; i < N; i++) {
        cout << i + 1 << " | ";
        for (int j = 0; j < N; j++) cout << state.board[i][j] << " | ";
        cout << endl;
        for (int k = 0; k < N * 4 + 3; k++) cout << "-";
        cout << endl;
    }
}

userInput getUserInput(const gameState &state) {
    while (true) {
        int inputZeile, inputSpalte;
        cout << "Zeile: ";
        cin >> inputZeile;
        cout << "Spalte: ";
        cin >> inputSpalte;
        cout << endl;

        if (!cin) {
            cin.clear();
            cin.ignore(1000, '\n');
            cout << "Ungueltige Eingabe, bitte nochmal." << endl;
            continue;
        }

        if (inputZeile >= 1 && inputZeile <= N &&
            inputSpalte >= 1 && inputSpalte <= N &&
            state.board[inputZeile - 1][inputSpalte - 1] == ' ') {
            return {true, inputZeile - 1, inputSpalte - 1};
        }

        cout << "Feld bereits belegt oder ausserhalb des Spielfelds." << endl;
    }
}

void checkforWin(gameState &state, int zeile, int spalte, char player) {
    int p = (player == 'X') ? 0 : 1;

    state.rowCount[p][zeile]++;
    state.colCount[p][spalte]++;
    if (zeile == spalte) state.diagCount[p]++;
    if (zeile + spalte == N - 1) state.antiDiagCount[p]++;

    if (state.rowCount[p][zeile] == N ||
        state.colCount[p][spalte] == N ||
        state.diagCount[p] == N ||
        state.antiDiagCount[p] == N) {
        state.running = false;
        state.winner = player;
        return;
    }

    if (state.filledCells >= N * N) {
        state.running = false;
        state.winner = '-';
    }
}

int main() {
#ifdef _WIN32
    SetConsoleOutputCP(CP_UTF8);
#endif

    gameState state;
    for (int i = 0; i < N; i++)
        for (int j = 0; j < N; j++)
            state.board[i][j] = ' ';

    int counter = 1;
    while (state.running) {
        render(state);
        char current_player = counter++ % 2 == 1 ? 'X' : 'O';
        cout << endl << "Am Zug ist Spieler: " << current_player << endl;
        auto [ok, zeile, spalte] = getUserInput(state);
        if (ok) {
            state.board[zeile][spalte] = current_player;
            state.filledCells++;
            checkforWin(state, zeile, spalte, current_player);
        }
    }

    render(state);
    if (state.winner == '-') {
        cout << endl << "Unentschieden!" << endl;
    } else {
        cout << endl << "Der Gewinner ist: " << state.winner << endl;
    }

#ifdef _WIN32
    system("pause");
#endif
    return 0;
}